[JeffB]

If you're successful with WiFi and USB, I'd expect the problem with the connection is related to the network settings on the PC for the LAN adapter.

It's likely you're pulling an IP address that matches the router when you connect by WiFi. USB always pulls 172.22.11.2 and creates a virtual network interface. Ethernet requires your PC to be setup to talk to the roboRIO. For this, modify the settings in Windows to make the computer's IP 10.TE.AM.# and subnet 255.255.0.0 and you should be able to communicate directly by Ethernet to the roboRIO.